1. Field of the Invention
The present invention involves replaceable subunits for Raster Input Scanning (RIS) or Raster Output Scanning (ROS) array bars, methods of fabricating these subunits and methods of fabricating extended arrays (RIS or ROS array bars) from these subunits, and particularly to subunits which include semiconductive substrates (or chips) having RIS or ROS components thereon and which are mounted on a support such as a daughterboard/heat sink assembly, each semiconductive substrate having a width greater than the width of each corresponding support so that the sides of the semiconductive substrate overlap the sides of the support.
2. Description of Related Art
Fabrication of pagewidth silicon devices, such as RIS arrays and ROS arrays from extended arrays of discrete subunits impose economically difficult fabricating processes on manufacturers because of the close tolerance requirement for the abutting edges of side-by-side subunits assembled to produce these pagewidth devices. RIS array subunits include, for example, Charge Coupled Devices (CCD's) which typically include a semiconductive substrate, made from silicon or gallium arsenide, having an array of photosites and supporting circuitry on one surface thereof. ROS array subunits include, for example, thermal ink jet printheads which typically include a semiconductive substrate (heater plate) made from silicon having a set of heating elements and passivated addressing electrodes formed thereon and an ink flow directing channel plate having parallel ink channels in communication with a manifold on one end and open at another end, aligned with and bonded to the heater plate, so that each ink channel contains a heating element. Two general architectures emerge in the design of large RIS or ROS bars using the subunit approach one in which all the subunits are located on one side of a substrate bar (which can function as a heat sink), and one in which subunits are staggered on either side of the bar. FIG. 1A shows a RIS or ROS bar 2 using the staggered approach wherein a plurality of subunits 6 are staggered on both sides of a substrate bar 4. FIG. 1B shows a RIS or ROS bar 8 wherein a plurality of subunits 6 are arranged on the same side of bar 4.
Using thermal ink jet printheads as an example, the advantage of the same side approach is that electrical and ink connections are simplified and thickness variations in the substrate bar do not introduce stitching problems (improper mating of adjacent characters produced by printhead subunits arranged on opposite sides of a bar having a variable thickness). A disadvantage of the same side approach is that it is difficult to remove defective or worn out subunits without disturbing or damaging adjacent subunits or the electrical connections of adjacent subunits to the daughterboard (which is formed on or attached to the heat sink substrate bar). The primary advantage of the staggered approach is that there is room between subunits so that individual subunits can be removed without damaging adjacent subunits.
U.S. Pat. Nos. 4,601,777 to Hawkins et al and 4,774,530 to Hawkins disclose carriage-type thermal ink jet printheads. These printheads include a channel plate having a plurality of nozzle-forming channels on a lower surface thereof which is bonded to the upper surface of a heater plate which includes a plurality of resistive heating elements so that a single resistive heating element is located in each channel of the channel plate. Each resistive heating element on the channel plate includes an addressing electrode having a terminal at one end thereof. The bonded channel plate and heater plate define a fully-operational thermal ink jet printhead. The printhead is attached to a daughterboard by bonding the lower surface of the heater plate to the daughterboard. The daughterboard also includes a plurality of electrodes each of which has a terminal at one end thereof to facilitate plugging into a female receptacle. The heater plate terminals are wire-bonded to the daughterboard electrodes so that each resistive element on the heater plate can be actuated by electronic pulses supplied to the daughterboard terminals. For an example of a printhead bonded to a daughterboard, see FIGS. 2 and 3 of the 4,601,777 patent.
U.S. Pat. No. 4,612,554 to Poleshuk discloses an ink jet printhead composed of two identical parts, each having a set of parallel V-grooves anisotropically etched therein. The lands between the grooves each contain a heating element and its associated addressing electrode. The grooved parts permit face-to-face mating, so that they are automatically self-aligned by the intermeshing of the lands containing the heating element and electrodes of one part with the grooves of the other part. A pagewidth printhead is produced by offsetting the first two mated parts, so that subsequently added parts abut each other and yet continue to be self-aligned. As shown in FIGS. 11 and 13 of this patent, each identical part which includes a plurality of resistive elements and associated addressing electrodes having terminals, is bonded to a flexible T-shaped board which includes a plurality of intermediate electrodes that are wire-bonded to the addressing electrode terminals. The T-shaped board is then mounted on an appropriate daughterboard, the intermediate electrodes being electrically connected to electrodes on the daughterboard.
U.S. Pat. Nos. 4,690,391 and 4,712,018 to Stoffel et al disclose a method and apparatus for fabricating full width scanning arrays. Smaller scanning arrays are assembled in abutting end-to-end relationship, each of the smaller arrays being provided with a pair of V-shaped locating grooves in the face thereof. An aligning tool having predisposed pin-like projections insertable into the locating grooves on the smaller scanning arrays upon assembly of the smaller arrays with the aligning tool is used to mate a series of smaller arrays in end-to-end abutting relationship.
U.S. Pat. No. 4,830,985 to Araghi et al discloses methods of fabricating image sensor arrays whereby smaller arrays containing, for example, photosites on one surface thereof are fabricated to have interlocking shapes which are used to accurately locate and align a plurality of smaller arrays on a substrate to form a long scanning array. The smaller arrays can be removed from the substrate by heating, lifting and sliding the smaller arrays relative to the substrate.